, 1887-06-15
Variable Stars.

Variable Stars.
Although the stars generally shine with
uniform brightness, there are among them
some remarkable exceptions to this general
rule. The earliest known and the most
remarkable amongst this class of Stars Is
one situated in the constellation CetuS,
and known by the name OF o Ceti, or Mira
Ceti. 1t has a period of nearly 33l days;
that is to say, it goes through its cycle of
variations in that length OF time, c%0ntinu'
ing for about ~ or IL daysa its maximum
brightness, which has at some of its maxi
ma, reached to the S 'coni order of magni.
tude; it then goes on decreasing for some
three months, until ~ becomes invisible,
in which condition it remains for five more
months, when it again goes on increasing
to the end of the period, when the maxim
um is again reached but the order of
magnitude is not always the same at sue.
ceSSive maxim. 1t is recorded, iii La
lande'S "A>tronomy, that be0ween
the years 1872 and 1916 this Star
was not visible at all. The month Of OctO-
Der is the best time for observing 1t. 1t
passes the meridian ut midnight about the
oath; and will be found in r.. A. 2h, BIN.
34s. and South DeelinatiOn 80 33. An
other remarkable variable Star is AlgOl,
HAS AAtNO ~ VI PNNAS 0'N 49,
quite three days-and ranges from the
second to the fourth magnitude. 1t con-
times at it's maximum for two days and q
half, then begins to decrease very sudden
~, aud i'll rather more than three hours is
reduced to q star of the fourth magnitude;
after remaining at this magnitude for ~
quarter of an hour, it again attains to its
maximum, III the same time that it took IN
passing from it to the minimum. This
star will be found in Right Ascension 3h.
ON. Ais. aud North Defamation 400 81. 1t
can be we'll observed in October and No
vember. It southS ab )ut midnight OF No
vember g.
The variable Star Beta Lyre is remarkable
in having a double period, viz, wO maxi
ma and two minima-the double period
being very nearly equal to thirteen days; the
difference between the maximum and mini
mum is only one degree of magnitude.
There is another popularity in the changes
of this Star,-that although the two maxi
ma are equal the minima are unequal. 1t
is situated in r. A. 18Th. 45n. 50S.,
and North Destination $50 La. The
bect time for observing it is i'll the
months of June and July. The Star Delta
Cephei is also subject TO considerable vari-
atoms in magnitude, passing from the
third to the fifth with a period of 81 days.
In passing from the minimum to the maxi
num-, it occupies less time than that re-
ouired for it to rcacl. the miuinum again
in the proportion Of 38 hours to Oh aeV 81
1t is to be found in II. A. 22h 24m. DDS.
and North Declinaiion $40 5Ot.-Angust
and September arc the best months III
which to, observe 1T. &}aal s5#e ,34a9
There are two hypothese suggested to ex.a
plain the phenomena exhibited by tue va.
riable or periodical Stars; one of which en-
deavours t. account for the. variations in
magnitude by %supposing that Opaque
bodies are revolving around these particn-
lar Stars, aud that at certain times they
are %interposed between the earth and the
Star, and so cut off from us a Fortien OF
the luminous rays of the latter. The other
hypothesis suggests that The stars them
selves may have portions of their surface
of unequal rejecting power, andathat in
their revolutions they pfesentoto us in
turns these more or less bright parts and
SO cause the variations that we observe